2,6-dinitrotoluene was separated from a mixture of 2,4-and 2,6-dinitrotoluene by a joint crystallization method. The method resolves effectively the separation and purification problems, which are difficult to be overcomed by recrystallization. The technological condition was improved by a series of experiments using different concentration of ethyl alcohol and get the best temperature by recrystallization with sulphuric acid in different temperatures.